Two-dimensional materials are research hotspots in recent years, and typical representatives include graphene and transition metal disulfides having semiconducting properties. A new two-dimensional material, black phosphorus, has appeared since 2013. Black phosphorus (BP) is a new form of elemental phosphorus generated from the reaction of white phosphorus under high temperature and high pressure. Different from white phosphorus having a tetrahedral crystal structure composed of four phosphorus atoms, the crystal structure of black phosphorus is rearranged under high temperature and high pressure, so that a great number of phosphorus atoms are connected with each other to form a regularly arranged planar structure (H. O. Churchill, P. Jarillo-Herrero. Nat. Nanotechnol. 2014, 9, 330). In this plane, each phosphorus atom is connected to the other three phosphorus atoms, and has a certain bond length and bond angle; the planes are stacked together by van der Waals force. This especial arrangement allows the black phosphorus to have better stability (white phosphorus and red phosphorus are likely to undergo spontaneous combustion in air, while black phosphorus is not like that) and more unique physical, chemical, biological and other properties, for example, variable band gap energy and good carrier mobility.
Like graphene, black phosphorus has excellent performances in mechanics, electronics, optics, thermotics, acoustics, and the like. Due to these properties, the study on black phosphorus is exploding in the past two years (H. O. Churchill, P. Jarillo-Herrero. Nat. Nanotechnol. 2014, 9, 330. L. Li, Y. Yu, et al. Nat. Nanotechnol. 2014, 9, 372. J. S. Qiao, X. H. Kong, et al. NatureCommun. 2014, 5,4475. D. Xiang, C. Han, et al. Nature Commun. 2014, 6, 6485. X. M. Wang, A. M. Jones, et al. Nanotechnol. 2015, 10, 517. J. Sun, H. W. Lee, et al. Nat. Nanotechnol. 2015).
Although black phosphorus has better stability than white phosphorus and red phosphorus, it still tends to be slowly oxidized by oxygen in water or air, thereby affecting its structure and function. Currently, the mechanism for which black phosphorus is oxidized has been clarified: phosphorus atom tends to react with oxygen to generate oxides of phosphorus, which in turn react with moisture in air to generate phosphoric acid (A. Favron, E. Gaufrès, et al. Nature Mater. 2015, 14, 826). The whole process will cause damage to the structure of black phosphorus, so that it would lose performance in electronics, optics, and the like. Therefore, how to solve the problem of black phosphorus susceptible to oxidation and to maintain the stability of structure and performance thereof becomes a key issue in the development of black phosphorus.
In order to solve the problem of oxidation of black phosphorus, various substances are coated onto the surface of black phosphorus in different ways by researchers, so as to block oxygen and moisture and reduce the opportunities of exposure of phosphorus atoms to oxygen and moisture: Wood et al. places black phosphorus on a silicon-based surface, and covers the upper surface of black phosphorus with oxides of titanium, gold and aluminum successively, so that the stability of black phosphorus is enhanced (J. D. Wood, S. A. Wells, et al. Nano Lett. 2014, 14, 6964); kim et al. places black phosphorus on the surface of Al2O3, and meanwhile covers the upper surface of black phosphorus with a layer of Al2O3, so that only the phosphorus atoms on the lateral side can expose to oxygen atoms, but the number of phosphorus atoms on the lateral side is quite small as compared with that of the upper and lower surfaces, and thus the antioxidant capacity of black phosphorus can be greatly enhanced (J. S. Kim, Y. Liu, et al. Sci. Rep. 2015, 5, 8989); Lee et al. deposits nanoscale titanium dioxide on the surface of black phosphorus by an atomic deposition process, so that the stability of black phosphorus can also be improved (H. U. Lee, S. C. Lee, et al. Sci. Rep. 2015, 5, 8691).
The core idea in the existing solutions is to coat other substances on the surface of black phosphorus to reduce the exposure of black phosphorus to oxygen and moisture, but its effect of eliminating the oxidization of black phosphorus is not satisfactory. Therefore, there is a need to find a new solution to eliminate the oxidation of black phosphorus.